From SwPatWiki

Every WikiGroup can have GroupHeader and GroupFooter pages that contain markup that should be included at the beginning or end of each page within the group. This feature is primarily used for:

adding a disclaimer or heading to all of the pages of a group

defining custom WikiStyles that may be used for all pages in a group

replacing the default headers and/or footers for pages in a group (using [[noheader]] and [[nofooter]] -- see SpecialMarkups)

To create a GroupHeader, just create a new page called YourGroup.GroupHeader. GroupHeaders allow WikiUsers to create groups with custom headers and footers without having to coordinate with a WikiAdministrator. For even more control, WikiAdministrators can do PerGroupCustomizations as a LocalCustomization.

A wiki page within a group can suppress the default GroupHeader or GroupFooter by using the [[nogroupheader]] and [[nogroupfooter]] markups.